I picked this little PEC square up a while back, probably due to someone mentioning it somewhere (although I can't remember who or where):
The price appears to be at near an all time high so I might consider waiting for it to drop back down..
I have to say that its an absolute gem. Its my go to tool for all sorts of things at this point. The layout lines are accurate to within my ability to measure them with any of my other tools (micrometers) and its square to as square as I can check square. Its just the right size for small layout and line transfers. It checks dovetail and other joinery cuts as being square as nicely as anything else I've got (and better than most). It works a champ as a small depth gauge.
Overall its just a super handy little measuring tool. Sometimes smaller is better.
I've been tempted to add the sterling dovetail rule option for it, that would allow checking narrow gaps for square easier. In practice it works pretty well by just tilting the blade and I'm not sure that adding this wouldn't be just adding to my metrology tooling obsession for minimal value.